Skip to main content

Full text of "Aquatic pests on irrigation systems : identification guide"

See other formats


Second Edition 




U.S. Bureau of Reclamation 

2800 Cottage Way 
Sacramento, CA 95825 











Second Edition 


By N. E. Otto, T. R. Hartley, 

and J. S. Thullen 

Illustrated by D. W. Cunningham 

and J. M. Evans 

Water and Power Resources Service 


As the Nation's principal conservation agency, the Department 
of the Interior has responsibihty for most of our nationally 
owned public lands and natural resources. This includes 
fostering the wisest use of our land and water resources, 
protecting our fish and wildlife, preserving the environmental 
and cultural values of our national parks and historical places, 
and providing for the enjoyment of life through outdoor 
recreation. The Department assesses our energy and mineral 
resources and works to assure that their development is in the 
best interests of all our people. The Department also has a major 
responsibility for American Indian reservation communities 
and for people who live in Island Territories under U.S. 

On November 6, 1979, the Bureau of Reclamation was 
renamed the Water and Power Resources Service in the U.S. 
Department of the Interior. The new name more closely 
identifies the agency with its principal functions-supplying 
water and power. 


Denver, Colorado 



For sale by the Superintendent of Documents, U.S. Government 
Printing Office, Washington, D.C. 20402, and the Water and Power 
Resources Service, Denver Federal Center, Denver, Colo. 80225, 
Attention: 922. 


Extensive infestations of obnoxious plants and certain aquatic 
animals cause problems on irrigation systems, such as reduction in 
carrying capacity of the system, increased evaporation and seepage, 
clogging of structures, adverse environmental impacts, and water loss 
through transpiration. Because of the many problems created by these 
growths, steps are usually necessary to control them or prevent their 

The methods employed to control these plants and animals differ 
widely due to differences in the organisms, such as growth habitat, 
organism metabolism, size, growth stage, and genetic characteristics. 
Correct identification of the organism is therefore important to the 
proper control recommendation. 

The simplified identification guide was prepared in response to 
requests from irrigation project operators and other personnel involved 
with biological problems requiring identification aids. It consists 
essentially of an illustration and a narrative description of some of the 
commonly observed organisms that become pests on the operation of 
irrigation systems in the Western United States. Not all animal pests 
that inhabit irrigation systems are included because many of these 
common ones such as muskrat, certain fish, and crayfish are readily 
recognizable by irrigation operating personnel. Some of the more 
serious and marginal ditchbank weeds have been included to illustrate 
a few typical problems on canals and drains. 

The narrative descriptions have been written primarily for use by 
Water and Power Resources Service field personnel and water user 
organizations directly concerned with the problems. They are not 
intended to be taxonomic descriptions of the species discussed. The 
illustrations include drawings of the entire organisms, with inserts to 
depict key identifying features, both vegetative and floral. Living 
material was used in most cases for reference in preparing the drawings. 
Individual species will vary in size, coloration, and other detailed 
features from those depicted. The overall characteristics illustrated are 
intended to show the field personnel sufficient features to permit a 
tentative identification. Should confirmation of this identification be 
needed, it is suggested that specimens be sent to a local experiment 
station or to the Chief, Division of Research, Code D-1522, 
Engineering and Research Center, Denver, Colorado, for examination. 

The information used in this booklet was obtained from various 
sources. A considerable portion of it has been derived from aquatic 
weed research studies conducted by the Water and Power Resources 
Service (formerly Bureau of Reclamation) in cooperation with the 

Science and Education Administration, U.S. Department of 
Agriculture, and the U.S. Fish and Wildlife Service. Information on 
the distribution of these aquatic pests and the problems they cause to 
irrigation or multiple use water systems has been obtained over the 
years through the cooperation of personnel of the Water and Power 
Resources Service and private irrigation districts. Many aquatic 
organisms were obtained from authoritative references listed in the 
bibliography. The authors wish to thank the many individuals whose 
contributions have made publication of this identification guide 

The original text was prepared by N. E. Otto, presently Supervisory 
Biological Scientist, and T. R. Bartley, chemist, both of the Division 
of Research, Engineering and Research Center; the final review and 
preparation of the original edition were performed by E. H. Larson, 
Division of Engineering Support, Bureau of Reclamation, Engineering 
and Research Center, Denver, Colorado. Also, the original illustrations 
were prepared by D. W. Cunningham of the Bureau of Reclamation, 
Lower Missouri Regional office in Denver. 

TTie additions and revisions for this second edition were authored 
by J. S. Thullen, Botanist, Division of Research, and edited by M. J. 
Cochran of the Technical Publications Branch, both of the 
Engineering and Research Center. The additional illustrations used 
in the second edition were prepared by J. M. Evans, Supervisor, 
Graphic Arts Unit, also of the Engineering and Research Center. 





Sago pondweed [Potamogeton pectinatus) 2 

Leafy pondweed {Potamogeton foliosus) 4 

American pondweed {Potamogeton nodosus) 6 

Curlyleaf pondweed {Potamogeton crispus) 8 
Richardson pondweed {Potamogeton 

Richardson//) 10 

Whitestem pondweed {Potamogeton praelongus) 12 

Giant pondweed {Potamogeton vag/natus) 14 

Horned pondweed {Zann/chell/a palustr/s) 16 

Waterweed {Elodea canadens/s) 18 

Hydrilla {Hydr/Ila vert/c/Uata) 20 

Waterbuttercup {Ranunculus spp.) 22 

Coontail ( Ceratophyllum demersum ) 24 

Watermilfoil (A/Kr/op/?7//f/i77spp.) 26 

Eurasian watermilfoil {Myr/ophyllum sp/catum) 28 

Waterplantain {Al/sma gram/neum) 30 

Holly-leaved waternymph {Najas manna) 32 

Waterstargrass {Heterantbera dub/a) 34 

Watercress ( Rad/cula Nasturt/um-aquat/cum ) 36 

True moss {Bryopbyta) 38 


Filamentous green algae 42 

Blue-green algae 44 

Stoneworts {Cbara spp. and N/teJIa spp.) 46 


Duckweed ( Z/e/77775 spp. and Wolff /a spp.) 50 

Waterhyacinth {E/cborn/a crass/pes) 52 

Alligatorweed {Alternantbera pb/loxero/des) 54 


Cattails ( Typha spp.) 58 

Bulrush {Scirpuss^^.) 60 


Reed canarygrass ( Phalaris arudinacea ) 64 

Johnsongrass {Sorghum halepense) 66 

Smartweed (/b^^o/7f//77spp.) 68 

Common reed [Phragmites communis) 70 


Tamarisk or saltcedar ( Tamarix pentandra.) 74 
Willow, Cottonwood, Russian-olive {Sal/x spp., 

Populus spp., Elaeagnus augustifolia) 76 


Freshwater sponge 80 

Pipe moss [Bryozoa) 82 
Freshwater clam (Asiatic clam) ( Corbicula 

fluminea) 84 

Black fly (5//77f///z//77 spp.) 86 




Submersed aquatic plants are a cosmopolitan group, representing 
a number of plant divisions and families. Plants grouped in the general 
submersed category range from primitive forms to highly developed 
flowering-type pondweeds that grow primarily in the water medium, 
including some species that develop specialized floating or emersed 
leaves and fruiting heads. A few representatives presented in this 
section might better be designated as combination submersed-emersed 
aquatic plants, but were included in this group because they are most 
troublesome when growing in the submersed form. Many of these 
plants are adaptable to wide variations in environment. The same 
species are often found growing in widely diverse situations of water 
temperature, quality, and velocity. Submersed aquatic plants often are 
able to survive periods of adverse growing conditions. This is due 
predominantly to prolific seed or spore production and the extensive 
and varied development of specialized tissue for vegetative 
multiplication. The submersed plants probably cause more trouble in 
irrigation waters than all other types of aquatic weeds. Extensive 
growths in distribution and drainage systems restrict the carrying 
capacity of canals and choke trashracks and pump inlets. 

Some of the more common species of submersed plants found in 
irrigation systems are described to illustrate the types that may be 
encountered. Positive identification of some of these plants requires 
close examination and the use of technical botanical references. 


Potamogeton pectinatus L. 

This pondweed has often been referred to as horsetail moss or 
bushy pondweed when observed growing in irrigation canals. The most 
widely accepted common name is "sago," meaning comblike, which 
is descriptive of its vegetative growth character. The species is probably 
the most widespread submersed aquatic weed found in irrigation canals 
of the Western United States. It grows in a variety of habitats from 
shallow, swift water to deep, still water and is often found in natural 
lakes, reservoirs, and streams, which are the main sources of infestation 
to irrigation systems. The vegetative form of sago pondweed is quite 
variable and will differ under changes in environment. A large, 
vigorous form of this species is often referred to as giant sago 

This plant produces a highly branched growth of slender stems and 
leaves arranged in a rather fan-shaped order. The plant produces only 
submersed leaves that are very narrow, linear, and somewhat triangular 
in cross section. Leaf tips are often long, tapering to points (insert 1). 
Flowers and the nutlike fruits are produced in an interrupted 
arrangement on a long, slender, terminal stem that floats at or near 
the water surface (insert 2). The plant is reproduced in subsequent 
growing seasons primarily by the vegetative tubers and occasionally by 
seed. Dissemination of tubers and fragmentation of vegetative plant 
parts can spread the plant during growing periods. The fleshy tubers 
(insert 3) are produced in considerable numbers at the ends of 
underground stems, or rhizomes, growing at depths from 0.1 to 1 
meter or more in canal soil. Occasionally, tubers are produced above 
the soil surface in the axils of stem branches. Because of the extensive 
rhizome runner and tuber development of this species, a single plant 
spreads over a considerable area. 


Potamogeton foliosus Raf . 

This plant develops a dense mat of slender, horizontal stems or 
rhizomes near the aquatic soil surface, rooting at each stem-joint or 
node. The erect stems develop to varying lengths depending upon the 
depth of water in irrigation canals. This species derives its common 
name "leafy" from the extensive foliage it produces. This pondweed 
is commonly found in canals and drains as an early season invader and 
sometimes in late season, but is not as prevalent during the 
midsummer. This is probably due to its inability to successfully 
compete with the more vigorous pondweed species, such as American 
and sago pondweeds where they coexist, and its early age of maturity. 

Leafy pondweed is completely submersed in habit, producing loose 
branches that present a bushy appearance with stems that seldom 
reach the surface in deep water. The leaf blades are narrow and flat 
and have a definite midrib vein that is white or yellowish in color. 
Flowers and fruiting spikes are produced on short stems arising from 
the terminals of the stems. 

The plant overwinters by producing a tight, compact vegetative 
bud in the axils of the branches that is rather hard when mature 
(insert 1 ). These winter or axillary buds are produced in considerable 
quantities as the plant progresses to vegetative maturity (insert 2) and 
sink to the bottom when the plant disintegrates. 

Leafy pondweed is widespread throughout the Western United 
States and is among the first pondweed species to invade an irrigation 
canal. It becomes overshadowed by more persistent deep-rooted 
pondweeds as the system ages, although it will continue to grow in 
association with these other species. It develops and matures rapidly 
during the warm summer months. Consequently, it is often found in 
intermittently watered canals and drains. As the plant reaches 
maturity, the stems fragment readily, producing considerable floating 


Potamogeton nodosus Poir. 

American pondweed is commonly found growing near the 
shoreline of lakes and ponds. Its presence becomes very obvious by the 
extensive development of floating leaves in midsummer. Its specific 
name, nodosus, inferring knotty, is a description apparently derived 
from the slight swelling at each stem-joint, or node, giving the plant 
stem a slight knotty appearance. This species infests laterals with 
low-velocity waters and the shallow areas of lakes, reservoirs, and ponds. 
This pondweed, although cosmopolitan in distribution, is most 
frequently found growing in irrigation laterals or in slow-moving water. 

The mature plant produces both submersed and emersed leaves. 
The submersed leaves are thin membranous structures that are long, 
narrow, and taper into the stem without a well-developed petiole (leaf 
stem). The mature submersed leaf is usually brownish-red in color but 
may, in deeper water, be more of a light green. 

Emersed or floating leaves are narrow-elliptical in shape, firm, and 
possess a definite waxy cuticle on the upper surface. Flowers are borne 
on a compact spike that emerges above the water surface for wind or 
insect pollination. Following development of the beaked nutlike fruit 
(insert 1 ), the spike turns down to submerse the maturing fruit head. 
The species spreads and is reproduced in subsequent seasons by long, 
slender buds that develop in chains on the terminals of horizontal 
stems (insert 2). Like sago pondweed, these vegetative winter-buds are 
produced in great numbers at depths of 0.05 to 0.30 meter below the 
surface of the aquatic soil. The winter-bud is easily distinguished from 
the terminal shoot buds by its makeup of overlapping fleshy scales. 

In growth habit, American pondweed resembles one or two other 
species of pondweeds. Differentiation can often be made only by the 
use of detailed botanical references. 


Potarnogeton crispus L. 

Curlyleaf pondweed is generally observed growing in slow-running 
streams or canals. This species has limited distribution in Western 
irrigation canals, being reported more extensively in the Central Valley 
of California. It is a well-marked species, deriving its specific name 
from the crisp nature of the mature leaves and overwintering buds. 
Stems of this plant are somewhat flattened (insert 1) and freely branch 
on the upper portions of the plant. This plant is completely submersed 
in growth habit, producing narrow oblong leaves with the leaf base 
attached directly to the main stem (sessile). The leaf margins are finely 
toothed, and upon maturity the margins become wavy, producing the 
characteristic indicated by the common name "curlyleaf pondweed." 

The vegetative overwintering bud that is produced in the leaf axil 
(insert 2) is unique to this species and provides a means of distinct 
identification. This burlike winter-bud (insert 3) is commonly 
produced in late summer. Upon maturity of the parent plant, these 
hard winter-buds fall to the bottom mud, where they develop in the 
subsequent growing season to produce new plants. 


Potamogeton Richardson ii Rydb. 

Richardson pondweed is usually found growing in deeper water of 
lakes and slower moving streams. It has occasionally been observed in 
large irrigation canals, but is seldom reported as being a serious 
problem to water distribution systems. 

This species has vegetative characteristics resembling those of two 
other pondweed species {P. praelongus and P. perfoliatus) that grow 
in similar habitats, and it may be a hybrid from these species. The leaf 
and stem growth characteristics of Richardson pondweed are quite 
distinct. The leaves of this plant are somewhat oval to linear, being 
thin and membraneous and clasping the stem at point of attachment 
(insert 1). All leaves are submersed and become progressively shorter 
toward the tip of a branch. Leaves have wavy margins and exhibit three 
to seven prominent veins that tend to parallel the long axis of the leaf. 
Stems and rhizomes are white and not spotted. Vegetative 
reproduction is from slender, fleshy winter-buds that develop under 
the soil on the terminals of horizontal stems (insert 2). These 
overwintering structures resemble those produced by American 
pondweed, but outwardly appear to be less scaly and are more fleshy 
and white in color. 

Flowers are borne on spikes that are produced near the water 
surface and may emerge. The beaked, nutlike fruits are produced on 
the flower spikes similar to American pondweed. 

This plant is widespread across the northern part of North 




Potamogeton praelongus Wulfen 

Whitestem pondweed, or praelongusas it is often called, is usually 
found in deep, cold water of clear lakes or irrigation conveyance 
systems near such water sources. It undoubtedly will be found more 
often in deeper canals, but has seldom been reported as a serious 
aquatic pest. The similarity of this species to a number of other 
pondweed species can be confusing to an identifier without 
examination for specific growth character. 

The large white or whitish stem that quite often grows in a zigzag 
pattern is distinctive (insert 1). Leaves of this species are oval to linear 
and are similar to Richardson pondweed in growth pattern, except that 
praelongusis generally larger and produces leaves with broad bases that 
never clasp the stem more than halfway. All leaves are submersed and 
become progressively shorter toward the tip of a branch. The tips of 
the leaves are boat shaped. The plant is produced from stoutish white 
rhizomes that are covered with rusty spots. 

Flowers and the strongly beaked nutlike fruits are produced on a 
spike that emerges above the water surface. 

This species is widespread across the northern part of North 
America and has been reported primarily from streams and lakes in 
the Pacific Northwest. 




Potamogeton vaginatus Turcz. 

This pondweed is undoubtedly often mistaken for the large 
vigorous form of sago pondweed that is commonly referred to as giant 
sago pondweed. Incorrect identification of this plant can be easily 
made because its vegetative growth characteristics are similar to those 
of sago. Only close examination can differentiate the two plants The 
stems of giant pondweed are freely branching and leafy. All the leaves 
are submersed and are narrow-linear in shape. In general, though, the 
leaves and stems of this species are larger and more robust than those 
of sago. 

There are a number of vegetative characteristics of this species that 
can be observed which can be used to differentiate it from other 
pondweeds with generally similar vegetative character. Like many 
organisms in nature, some of the identifying features given for giant 
pondweed can vary from those illustrated in this booklet. One of these 
which typifies the situation is the loose, leaf-sheathlike structure or 
stipule produced on the lower or primary leaves (insert 1 ) of giant 
pondweed; botanical descriptions indicate that this characteristic is 
sometimes approximated in sago pondweed. The leaf tips of giant 
pondweed are rather blunt and sometimes slightly notched (insert 2), 
unlike the sharp, tapering tip of sago. Flowering spikes of giant 
pondweed are more numerous and in more crowded whorls than those 
found on sago. 

One feature that should aid materially in the identification of this 
species is the uniquely shaped tuber, which is much different than the 
sago tuber (insert 3). These tubers are produced in knotty clusters on 
the terminals of fleshy white underground stems. 

A third pondweed species, P. filiformis, is closely related to both 
giant and sago pondweed and could be mistaken for giant pondweed. 
In general, P. filiformis, or fine-leaved pondweed, is less vigorous and 
has smaller leaves, stems, and tubers, although the tubers are similar 
to those produced by P. vaginatus. 

Giant pondweed is seldom reported in Western irrigation systems, 
but probably occurs more often than suspected because of its similarity 
to the cosmopolitan sago pondweed. 




Zannichellia palustris L. 

Horned pondweed is a cosmopolitan plant that is classified in a 
different plant genus than the other aquatic weeds referred to as 
pondweeds. The Zannichellia genus has one species only. This plant 
resembles sago pondweed, but upon close examination many 
differences can be noted. Leaves of horned pondweed are much 
narrower and threadlike and arranged on the stems in an opposite 
manner, while those of sago pondweed develop from the stems in an 
alternate pattern. This is a completely submersed plant that develops 
a dense, creeping system of horizontal stems that are shallow rooted 
with sparsely branching stems. It produces a dense, usually short, mass 
of vegetation. 

The plant derives its common name from the incurving hornlike 
beaked fruits (insert 1) which are usually found in threes or fours with 
very short fruit stems (peduncles). Flowers and fruits are produced in 
the axils of the leaves (insert 2). Unlike true pondweeds of the 
Potamogeton genus, this plant does not produce vegetative 
overwintering structures and is carried through adverse growing 
conditions and disseminated by seed. 

Horned pondweed is a widespread aquatic weed and can most often 
be observed in spring or early summer, preceding the growth of other 
more vigorous pondweeds, although it will grow in association with the 
true pondweeds. Horned pondweed is rather unique in that it will 
tolerate excessively cold water and can often be seen growing as small 
tufts on the bottom of streams and canals of Northern latitudes during 
winter months. 




Elodea canadensis Michx. 

This completely submersed plant is often seen growing in dense 
patches in all types of freshwater habitats. It is commonly referred to 
as waterweed, water-thyme, or ditch-moss. Also, the generic name 
Elodea, a derivation of the Greek e/oc/e^ (meaning marshy), is 
becoming an increasingly popular name for plants in this genus. 
Anarcharis and Philotn'a are synonymous names for this plant genus 
that are falling into disuse. The plant is probably an escapee from 
ornamental culture in aquariums. 

There are a number of species of this genus, but E . canadensis is 
the most widespread in irrigation waters. The vegetative growth habit 
is distinct, making identification of the genus quite easy. Species 
identification becomes more laborious but does not require detailed 
study. The slender stems branch readily into paired forks with whorls 
of leaves three or four in number at each stem node. Individual leaf 
bases are somewhat clasping, forming a continuous ring around the 
stem (insert 1). Leaf margins are small toothed. Male and female 
flowers are borne on separate plants. The pistillate or female plant is 
the one seen most often, producing leaf whorls that are more dense 
with shorter stem intemodes than those on the male plant. 

The waterweed flower is produced quite often on the end of 
threadlike shoots that grow to the water surface. Fruits and seeds are 
rare because of the scarcity of male plants. Dissemination of the plant 
is from vegetative buds produced on the terminal ends of shoots and 
by plant fragmentation. The plant overwinters by these vegetative 
buds that break from the stems in late summer and fall into the bottom 
mud (insert 2). This plant will survive and grow in a completely floating 
state, although it usually grows much more vigorously when rooted in 

Waterweed is very common to practically all areas of Western 
irrigation systems and can be found growing in patches in both large 
canals and small laterals. It will produce very dense stands in 
slow-moving water of canals and shallow areas of reservoirs and ponds. 





Hydrilla verticillata Royle 

Hydrilla is an extremely prolific aquatic plant that has infested 
millions of acres of lakes, rivers, and irrigation systems throughout the 
United States. The plant is not a native species. Thought to have been 
imported originally for aquarium use, it was first discovered in a Florida 
river and drainage canal in 1960. 

Hydn'llahdiS two to eight leaves per whorl along its long branching 
stems. The leaves are spear shaped, the length is approximately five 
to seven times the width, and the leaf margins are serrated. Hydrilla 
is often confused with waterweed {Elodea canadensis ^\c\\\.) which 
has very similar vegetative growth habits. However, several 
characteristics distinguish the two species ( 1 ) Hydrilla has one to three 
tiny spines along the central vein on the underside of the leaves, which 
waterweed lacks; (2) Hydrilla leaf margins are serrated, but waterweed 
leaf margins are either smooth or finely serrated (insert 1); (3) Turions 
form in the axils of hydnlMeaves (insert 2); and (4) Potato-like tubers 
appear in the soil on the ends of the rhizomes (insert 3). Waterweed 
produces neither turions or tubers. 

Hydrilla zho produces small, white female flowers (insert 4) which 
appear as six simple pedals at the end of a long threadlike stalk. They 
may be observed on or near the water surface in late summer or early 
fall. Male flowers, and consequently fruits, have not been observed in 
the United States. 

Hydrilla reproduces by vegetative fragments, stolons, turions, and 
tubers. Control efforts are very difficult because turions and tubers are 
able to survive winter and stress periods. 




1 ^ 


1^ « J^^ 






^^H ^^^^ 




^ 1 

Hydrilla verticillata 



Ranunculus spp. 

Plants in this genus are not necessarily true submersed aquatics, 
but are amphibious, growing as well on damp soil as in the submersed 
condition. These plants are represented by both annuals and perennials 
having alternate leaves on either erect or creeping stems. Often in the 
emersed forms, the leaves will arise from a basal or rosettelike point 
of attachment. Submersed leaves are finely dissected or with divided 
lobes running to common points on the leaf stem (petiole), giving the 
appearance of a crow's foot (insert 1). The emersed leaves, which are 
not always present, vary with species, and are broader and less finely 
divided than submersed leaves. 

Flowers are produced above the water surface. The flower petals 
are usually yellow and rarely white. Some aquatic forms produce 
flowers that have white sepals (the leaflike structures on the basal 
portions of flowers) and yellow petals, giving the appearance of white 
flowers with yellow centers. Various species produce solitary flowers, 
while others develop in clusters. The beaked nutlike fruit pods are 

Crowfoot is often found in irrigation systems, usually in clear, 
low-velocity waters. It seldom develops extensively enough to create 
a serious hydraulic problem. Waterbuttercup has been reported to be 
a plant indicative of good water quality, as it apparently will not 
tolerate adverse conditions as readily as many aquatic weed species. 




Ceratophyllurn demersum L. 

This perennial plant is found in sluggish streams and ditches and 
is among the dominant aquatics in temporary ponds and newly formed 
lakes. These are rootless plants that in early season grow upright, with 
the lower portion anchored in the bottom mud. During late season 
the plants are found floating near the surface. The finely divided leaves 
are produced in whorls at stem nodes. The individual leaf is cut into 
two to four forked divisions with occasional toothlike projections on 
the margins (insert 1). The stem internodes are shortened toward the 
tip, giving the shoot an appearance of a bushy tail, hence the common 
name "coontail". 

Flowers and fruits are produced singularly in the axil of the leaf 
whorls. The fruit is rarely observed. Vegetative overwintering is 
accomplished by thickened and shortened shoot tips that develop late 
in the season and break off and sink to the bottom soil to vegetate 
during favorable growth periods. 

This plant can be confused with certain submersed water 
buttercups without some scrutiny. The two plants can be distinguished 
by the definite whorled leaf attachment and forked divisions of 
Ceratophyllurn , unlike the fan-shaped submersed leaves of buttercup. 

Coontail, while not generally considered a serious submersed 
aquatic weed, is often seen in irrigation systems and can be an aquatic 
pest in small laterals and new systems. 




Myriophyllum spp. 

Watermilfoil may be completely submersed with just the flowering 
spikes emersing, or in certain species portions of the stem and leaves 
may be above the surface. The stems are simple or slightly branched, 
and the leaves may be arranged either in whorls or scattered on the 
stem. The submersed leaves are usually highly dissected and comblike. 

One of the more commonly observed species is the American or 
northern milfoil, Myriophyllum exalbescens Fern. Stems of this 
species are simple or forked, with vegetative tissue that has a 
brownish-purple pigmentation. The deeply dissected leaves develop in 
whorls of threes or fours (insert 1). The floral spike is the only plant 
part that emerges above the water surface. Parrot-feather, 
M. brasiliense Cambess, is a species that is occasionally seen as an 
escapee from aquarium culture, especially in warmer climates. This 
species produces emersed leaves that are featherlike and are dissected 
into 10 or more comblike divisions (insert 2). Flowers of parrot-feather 
are usually conspicuous as white tufts in the axils of the emersed leaves. 

Flowers on all the species are quite small, having four petals. The 
fruits are nutlike bodies joined in groups of four. Certain species 
overwinter by means of winter-buds that develop in the leaf axils. 
Because of the wide variability of foliage character of plants in this 
genus, even on the same plant, it is difficult to separate the species. 
Differences can only be determined by detailed study of flowers and 

Watermilfoil is a widely distributed aquatic plant that is often 
found on irrigation systems, particularly in still or slow-moving water. 
It is considered to be a pest to water distribution systems only in 
localized situations. 




MyriophylluTn spicatum L. 

Eurasian watermilfoil, like the northern watermilfoil 
{Myriophyllum exalbascens), is completely submerged except for the 
flowering spikes. The stems are branched slightly and can vary in color 
from a pale greenish-yellow to a full pink. The leaves are separated into 
12 to 24 pairs of filamentlike divisions (insert 1) and develop on the 
stem, usually four in a whorl. Northern watermilfoil's leaves are similar 
but usually have 14 or less pairs of divisions. The flowers are small and 
are usually in whorls of four along a slender terminal spike which 
extends above the water surface. All but the lower two to four whorls 
of floral bracts (leaves beneath and enclosing the flowers) have smooth 
edges and are shorter than the flowers and fruits. The lower floral 
bracts have comblike or serrated edges and are longer than the fruits 
(insert 2). The lower bracts of the northern watermilfoil are serrated, 
but are usually shorter than the fruits in length. The nuflike fruits of 
the eurasian variety have exhibited long periods of dormancy and 
erratic germination. Winter buds, apparently, are not produced. 

Eurasian watermilfoil has become a nuisance in lakes, streams, and 
irrigation systems in recent years. It colonizes new sites mainly by 
vegetative fragments which develop roots, sink, and establish new 
plants. This fragmentation is responsible for the rapid spread of this 
weed and the difficulty in controlling it. 




Alisma gramineum var. Geyeri Samuelsson 

Plants in this family can be seen growing emersed, totally 
submersed, or on wet banks. The species that is illustrated produces 
both emersed and submersed vegetation. It is probably more 
commonly observed in irrigation canals as a submersed plant. Possibly 
when it develops the emersed form, it might be thought of as being 
a totally different plant. 

In a submersed habit this plant produces long linear or grasslike 
leaves for which the specific name gramineum , or grasslike, is 
descriptive. The leaves arise from the base or crown, attaining lengths 
up to 900 millimeters. Roots of Alisma are fibrous and generally do 
not extend deep into the mud. In the emersed habit, the narrow, 
elliptical-shaped leaf blades emerge above the water surface supported 
by long, firm petioles (leaf stems). 

Flowers of this plant are borne on a loose, irregular forked 
arrangement or loose panicle. Flower petals are white to purplish. The 
individual seed heads or nutlets are borne in a ring (insert 1). 
Differentiation between varieties of this species is made by the length 
of the fruiting stems, Ce/e/v having fruiting stems shorter than the 

Alisma may be annual or perennial. These plants produce many 
viable seed that readily germinate in a wet or submersed situation. 
However, the seedling survival is generally low as apparently only a 
fraction of the germinated seedlings are able to reach maturity. 
Waterplantain overwinters by means of a fleshy crown or cormlike 
structure when exhibiting perennial growth habits. 




Najas marina L. 

This member of the A'^/^c/ family is easily recognized by its 
spiny-stiff leaves that resemble the leaf of holly. 

Stems of this completely submersed species branch loosely near the 
plant base. The stem internodes are often armed with prickles. The 
stiff leaves are oblong to linear with coarse spiny margins, and are often 
spiny toothed along the back of the midrib vein (insert 1). The leaf 
bases are rounded and broad, forming a conspicuous sheath at the 
stem. Flowers and fruits of this annual plant are produced in the 
sheathed base of the leaf axils. The fruit is a nutlet enclosed in a loose 
membrane-like covering that is easily separated. 

Holly-leaved Naiad, as it is sometimes called, may be found in both 
deep and shallow alkaline water. It is apparently not widespread or 
commonly found, but has been reported as an invader in irrigation 
canals of the Southwest. 




Heteranthera dub/a Jacq. 

The leaf and stem tissue of this submersed plant could easily cause 
it to be mistaken for a pondweed were it not for its light yellow starlike 
flowers (insert 1). The star-shaped flowers are produced singularly on 
elongated tubelike stems that are exposed above the water surface 
(insert 4). Leaves of waterstargrass lack a midrib vein and are grasslike 
with bases attached directly to the branching stems (insert 2). The leaf 
sheaths are thin membraneous and tipped with small, pointed 
appendages (insert 3). 

There is a form of this plant that produces shorter leaves and stems 
and grows on shallow mudbars. This form is reported to flower more 
often than the submersed aquatic type. The genus Heteranthera is 
sometimes commonly referred to as mud plantain, probably because 
of the ability of various species to survive on mudbanks. 

Waterstargrass grows in both still and flowing waters. Although it 
is widespread in the Midwestern and Southeastern States, it is not 
commonly seen in Western irrigation canals. It has been reported most 
extensively in canals of Arizona and occasionally in California. 




Radicula Nasturtium-aquaticum L. 

Watercress is a widespread perennial herb that is seen growing on 
margins of small streams and shallow water areas. This particular 
species is the common watercress that is collected from fresh springs 
for salads. Because of the creeping and freely rooting stem growth 
habit, watercress can extend into the shallow, slow-moving water of 
irrigation canals and obstruct waterflows. This plant is a troublesome 
weed in irrigation drainage channels when not kept in check. 

Watercress is quite easily recognized by its fleshy leaf structure that 
is made up from three to nine oval-shaped leaflets that combine to 
form a single compound leaf. The plant roots extensively from the 
prostrate stems. Small flowers with petals are produced at the terminals 
of the stems. The slim fruit pod, or silique, which is typical of plants 
of the mustard family will be seen below the flower heads, the older 
ones elongating as the seeds mature. 

This plant extends its growth from the shallow shore margins into 
the water, often completely submersed for long periods. 

Species of watercress are widespread and can be expected to be 
found on wet areas of all Western irrigation systems although usually 
in localized infestations. 





Many submersed aquatic plants are commonly referred to as moss, 
which is botanically incorrect and leads to confusion in obtaining 
information on control measures. Mosses or Musci {txwt mosses) 
belong to the plant division BryophytasLud are a higher type plant than 
filamentous green algae with which they are often confused. 

The conspicuous plant, or gametophyte, of commonly observed 
mosses is differentiated into an erect central axis or stem with small 
spirally arranged leaves resembling those of true flowering plants. True 
mosses do not have roots, but are anchored to the substratum by 
threadlike projections, or rhizoids, that fan out from the base of the 

True mosses are predominantly land plants, being one of the 
simpler types of green terrestrial plants. A few species are aquatic or 
semi-aquatic in growth habit and vary in size. Generally, true moss 
produces short stems only a fraction of an inch in length that arise 
from dense mats of growth. A few representatives are much larger, 
producing stems up to 150 to 200 millimeters in length. 

True mosses are occasionally found growing on small areas on canal 
linings, often in the shaded areas, and where a thin soil substrate is 
available. They occasionally are reported to cause problems to water 
distribution systems. Two genera of mosses have been reported in 
Western irrigation systems, although many others undoubtedly occur. 
These genera are Fontinalis, which is one of the largest mosses, and 
Fissidens y a much smaller plant. A typical growth of the moss 
Fontinalis is shown as it might be found on a lined canal. 




Algae are microscopic plants that are included in the botanical 
division Thallophyta, being unlike higher flowering plants in that the 
plant tissue is not differentiated into stems, roots, and leaves. The plant 
body is referred to as a thallus. Sometimes plants of this division that 
grow in irrigation systems are incorrectly called moss. True mosses, as 
previously described, are a much higher type plant. 

There are a multitude of types and species of algae that grow in 
freshwater. The type most generally considered to be important in the 
operation of irrigation systems is the filamentous green algae. These 
are considered to be of a higher botanical type, but still are very 
primitive compared to the flower-producing pondweeds. 

A number of microscopic or more primitive one-celled algae (that 
are either unicellular or colonial) are usually found in irrigation waters 
and often create the problem of reducing the carrying capacity of water 
distribution systems. These algae range from green types to blue-green 
types, often causing the water to be murky or green in appearance, 
or produce distinctive colonies that vary widely in character. Some of 
these algae are responsible for odors and tastes in water and some can 
be toxic to animals when ingested. Certain higher forms of green algae 
develop a thallus that bears a certain resemblance to the leaf and stem 
tissue of higher plants. These plants, known as stonewarts or Chara, 
are discussed in a later section. 



Filamentous green algae present serious problems in irrigation 
canals by attaching to concrete canal linings, thus reducing the 
carrying capacity. A typical habitat sketch of attached filamentous 
green algae is shown in the upper portion of the illustration. 

A close visual examination of these attached organisms (insert) 
reveals that these plant colonies are composed of masses of threadlike 
structures. Some species of green algae produce filaments that are 
coated with a gelatinous sheath, giving them a slimelike texture. 
Certain other species are covered with calcareous deposits that impart 
a rough, coarse texture. The individual plant body, or thallus, consists 
of a single row of cells that divide longitudinally to produce fine, green 
filaments. Some species develop solitary filaments, while the more 
complex ones are diversely branched. The filaments of certain species 
attach to a solid substrate, such as a canal lining, by a special cell called 
a holdfast. 

Filamentous green algae multiply vegetatively by cell division and 
fragmentation of the threadlike thallus. Thick-walled microscopic 
spores, or resting bodies, provide a means for the plant's survival during 
unfavorable growing conditions and for dissemination of the species. 

Identification of the individual genera of algae is often difficult and 
requires detailed microscopic examination. Single species of algae are 
seldom found growing alone in a field situation, but a number of 
species usually grow in association with one another. Some of the more 
common genera found in irrigation systems are Stigeoclonium , 
Oedogonium , Ulothnx, and Cladophora . Magnifications of the 
growth characteristics of these few genera are illustrated in the lower 
portion of the plate to give some concept of the cellular makeup of 
these microscopic plants. 

Many of the filamentous green algae also will develop colonies of 
filaments that are free floating. These develop so extensively as to 
produce dense mats at or near the water surface. Usually, in these 
growth states, the algae become a nuisance by fouling pump inlets, 
irrigation siphon tubes, trashracks, and sprinkler heads. 





















Blue-green algae are a very diverse group, being classified primarily 
by cell pigmentations that produce an overall bluish-green coloration 
to the plants. These plants, like green algae, grow as individual cells 
(unicellular) or in filamentous colonies, depending on genera. Many 
of the filamentous colonial types produce gelatinous coatings that 
sheath the cell walls. A number of species produce colonies, such as 
the jelly-balls of Nostoc and the tough, compact mats of 
Phormidium . Blue-green algae are usually found growing in 
association with filamentous green algae. A few typical blue-green algae 
found on irrigation systems are illustrated; a habitat sketch is shown 
on the left and a microscopic view of the plant cells that make up the 
filaments on the right. 

The upper left portion of the drawing shows the typical "jelly-ball" 
of Nostoc, which will be highly variable in size and is observed either 
free-floating or resting on the bottom of a canal or pond. These algae 
can cause problems in plugging siphon tubes and pumps. 

The second illustration shows free-floating Aphanizomenon 
colonies. This species gives an impression of lawn grass clippings 
floating in water. This plant could, in certain situations, become a 
menace to mechanical water conveyance equipment, as well as create 
a taste-odor problem to potable water. 

One of the blue-greens that has caused some hydraulic problems 
to lined conveyance channels is Phormidium . Colonies of this species 
can become fixed to a canal lining and produce thick, tough, gelatinous 
masses, thus not only reducing the capacity of the channel but causing 
fouling of pumps, hydroelectric generators, and siphon tubes as the 
mats break apart. 

The lower illustration is Anabaena, a species that can, upon 
decomposition, produce taste-odor problems as well as soluble 
substances that can be toxic if ingested in quantity by mammals. This 
is a very common species frequently found floating on the water 
surface in dense gelatinous masses that have a rather moldy 




Chara spp. and Nitella spp. 

This is an interesting family of plants represented by the most 
common genera Chara dnidi Nitella. These plants are universally 
recognized as being related to green algae, but technically there exists 
a diversity of opinion by botanists as to the degree of relationship. 

These gray-green plants are more highly developed vegetatively 
compared to most other freshwater algae. They grow submersed in 
freshwater upon muddy or sandy bottoms, thriving best in clear, hard 

This family of algae is unique in that the plant body or thallus is 
characterized by a branched erect stem that has cylindrical whorls of 
branches at regular successions along the stem. Each stem node bears 
these leaflike branches that give the plant the general appearance of 
being a higher or flowering-type plant. 

Each internode (stemlike tissue between the leaf whorls) of the 
stem consists of a single cell in Nitella , while in many species of Chara 
the internodal cell is sheathed by a layer of vertically elongated cells 
of much smaller diameter (insert 1). These sheathing cells give the 
Chara stem a vertically lined appearance, while Nitella is smooth. 

These plants reproduce both vegetatively and by sexual fruiting 
bodies. The female body or oogonium (egg-bearing case) is quite 
conspicuous and its whorl of cap cells differ in number between genera 
(insert 2). Both the female and male fruiting bodies are borne on the 
leaf filaments. Vegetative propagation is accomplished by star-shaped 
aggregates of cells that develop on the lower stem nodes, bulblet-like 
structures on the anchoring rhizoids, or anchoring structures and 
outgrowths from the stem nodes. 

Many species, especially those of Chara, become encrusted with 
calcareous deposits giving the plant a harsh, rough surface. This 
calcium carbonate accumulation around the plant may remain intact 
after death of the plant, giving rise to the name "stonewort" or stone 

These plants may present problems in water distribution systems, 
but seldom become as serious a weed pest as the filamentous green 
algae. They rapidly become established in small pools and in standing 
water on new irrigation systems. 




A number of floating plant pests are known to exist on Western 
irrigation systems. Some of these plants can survive either completely 
free-floating or they may root in the bottom mud when growing in 
shallow waters. Certain species are almost amphibious and will extend 
onto mudbanks. Fortunately for Western irrigation systems, a few of 
the very aggressive species will not survive freezing temperatures and 
occur only in isolated areas in the Western United States. Two of these 
are waterhyacinth and alligatorweed. These species are illustrated to 
acquaint the irrigation operator on more southerly projects with them 
in the event these plants should extend their range. 

Duckweed, a very cosmopolitan floating aquatic weed, is included 
to illustrate a typical plant of this group. A number of plants 
representing many plant families are true-floating aquatics and do 
occur on Western irrigation systems, but were not included because 
of the very limited problems they produce. Some of these species found 
in isolated areas in the West are waterlettuce, watervelvet, 
waterprimrose and waterfern. The reader is referred to publications 
cited in the bibliography for aid in their identification in the event 
they might be encountered. 



Lemna spp. and Wolffia spp. 

Duckweeds are characterized by their diminutive size and lack of 
stems and true leaves. They are the simplest and some of them the 
smallest of flowering plants. Duckweeds are free-floating on or slightly 
beneath the water surface. The plant consists of a leaflike structure, 
or frond, and in some species a single root that penetrates into the 
water. The flowers, being inconspicuous and simple in structural form, 
arise from the edge or upper surface of the fronds. These are seldom 
seen and some species apparently never flower. 

This family of plants has four genera, of which Lemna is probably 
most often seen on irrigation systems where water is static. A typical 
vegetative habitat of this species is shown, consisting of hundreds of 
plants covering the surface of very slow moving or quiet waters. Lemna 
minor L., as illustrated, is one of the smaller species. A single frond 
of this plant is about the size of a pinhead. Plants of the Wolffia gtnxis 
have fronds much smaller than Lemna and are microscopic in size. 
They can be detected by the greenish cast they impart to the water 
surface. Plants in this family propagate vegetatively by proliferous 
growth of new individuals from the edge or base of the parent fronds. 
During warm summer months these plants can cover the surface of 
a pond in a few weeks. The plant overwinters both by seed and 
vegetatively by a minute bulblet frond that sinks to the bottom of the 
water body and rises to the surface the following season. 

These plants become pests to irrigation systems when they are 
carried into siphon tubes, trashracks, and pump inlet structures from 
their still water habitat. 




Eichornia crassipes Mart. 

Waterhyacinth is a native of tropical America and was probably 
introduced in the United States as an ornamental. As an escapee it 
has become an exceedingly troublesome species by clogging waterways 
of the Southern States. Its attractive blue-purple flowers and 
characteristic bulbous leaf stem with rounded leaf blade make it easy 
to identify. The plant is usually found floating on the surface of ponds 
and quiet streams and growing on mudbanks. This plant spreads 
vegetatively by horizontal stem growth and rooting at the nodes to 
produce new plants that develop into mats covering large areas. The 
capsule-like fruits contain many seeds that provide for extensive spread 
of the species in suitable climates. 

Fortunately for Western irrigation systems, this plant is unable to 
withstand temperatures of Northern latitudes and is only occasionally 
found in Western States of milder climates. Waterhyacinth has been 
locally abundant in a few localities in California for a number of years, 
but has apparently been kept in check and is seldom reported as an 
aquatic weed in areas of Water and Power Resources Service activity. 




Alternantbera philoxeroides Mart. 

Alligatorweed is native of tropical regions and has become a serious 
pest covering extensive drainage and ponded areas in the Southern 
States. It has been introduced northward, but is not hardy in the 
Northern States. 

This is a spreading weed that forms floating mats over extensive 
areas sufficiently dense to support the weight of a man. The creeping, 
branched, prostrate stems are often jointed, and roots form extensively 
at stem-joints. During low water it will cover muddy banks and 
lowlands. The linear leaves develop on the stems in an opposite 
arrangement with smooth or entire margins, and are somewhat waxy 
in appearance. Flowers are produced in a rounded compact spike. The 
flower sepals or flower leaves are pale green or whitish, giving the 
flower spike an overall white appearance. 

Like the waterhyacinth, this weed is unable to withstand extended 
periods of freezing; consequently, it is seldom found on Western 
irrigation systems. It has been reported to occur in small localized areas 
of the Southwest. 




Many plant pests that root in the aquatic soil and send stems and 
leaves above the water surface are grouped in this category and are well 
known to irrigation operators. Some of the species in this group are 
the first to invade newly inundated lands, especially when the features 
are intermittently wet or where the water is normally shallow. 
Backwater areas of reservoirs and drainage canals are especially 
troubled by these weeds. The cattail and bulrush species, which are 
illustrated, typify these plants. A number of additional species are 
known to infest such environments, but vary locally and are too 
numerous for inclusion in this booklet. 

Emersed weeds are especially troublesome to irrigation systems in 
that they spread rapidly to choke drainage channels, increase silt 
deposition, interfere with designed operation and maintenance 
procedures, and waste tremendous quantities of water through natural 
life processes of transpiration. 



Typha spp. 

Cattails are widely distributed and are well known. They will invade 
almost any wet place, being one of the first plants to occupy a newly 
inundated area. They are quite easily recognized by their growth of 
stout jointless stems, linear flat leaves, and cylindrical flower spikes. 
These plants produce fleshy underground stems that will spread a 
single individual over an extensive area. These underground stems or 
rhizomes also perform as food storage organs, having a high starch 
content. The cattail rhizome is readily eaten by aquatic animals, such 
as muskrats. 

The two species most commonly observed are T. latifoliaL., the 
common or broadleaf cattail, and T. angustifoliaL., the narrowleaf 
cattail. When these two species occur together, a certain amount of 
hybridization will produce individuals of divergent character. 

Identification is readily accomplished by study of the flower spikes, 
which consist of two portions; the female or pistillate portion of the 
spike is below, and the male or staminate portion is above. The 
broadleaf cattail is recognized by its more persistent pistillate or 
seed-producing flowers, which are on the lower portion of the brown 
flower spike that is tail-like in appearance. The male portion of the 
flower spike is smaller in diameter, less compact, and soon disappears 
in midsummer leaving a tapered stem. The narrowleaf cattail, from 
its common name, is recognized by its more slender leaves and a 
definite separation that occurs between the male and female parts of 
the flower spike. This characteristic is clearly seen in the younger 
flower and becomes less definable as the seeds mature. 

Each flower spike will produce hundreds of seeds that are 
disseminated by air and water over wide areas to spread the species. 

Cattails are found on most Western irrigation systems and are 
especially troublesome in drains and slow-moving water of shallow 
channels. These plants will spread throughout a drain in a short time, 
thereby reducing the potential carrying capacity and increasing silt 




Scirpus spp. 

The bulrush, or club rush, belongs to the sedge family, Cyperaceae. 
These grasslike or rushlike herbs are generally perennial and rarely 
annual. They spread vegetatively and overwinter by means of scaly, 
stout, reddish horizontal stems or rhizomes. These plants are 
characterized by the cylindrical or variously angled erect stems 
(technically called culms) and much reduced small leaves that develop 
near the plant base. Leaves are often overlooked because of their 
reduced size and clasping nature in some species. 

There are numerous species of bulrush, but one of the more 
commonly observed species is the great or soft-stem bulrush, Scirpus 
validus\2^\\, that is often referred to as tule. This species has a soft, 
easily compressed culm (stem) that is round in cross section tapering 
upward. The flowers are produced on the terminal of the culms. These 
stems often grow in excess of a thousand millimeters in height. The 
leaves are sheathlike at the base of the plant. Accurate identification 
of the bulrushes requires detailed botanical study to differentiate the 
numerous species predominantly by means of flower and fruit 

Bulrush is common to irrigation projects, especially in marsh areas 
or in shallow drains. Their habitat is similar to the cattail, and they 
contribute extensively to the marshy vegetation complex that restricts 
the carrying potential of drainage conveyance channels. 




Weeds that grow along the margins and banks of irrigation systems 
are the most serious problem for irrigation operators, other than 
submersed aquatic weeds. Marginal weeds include a wide variety of 
grass and broadleaf species. They may also grow along lake and 
reservoir shorelines. 

Dense stands of plants such as reed canarygrass and johnsongrass 
restrict irrigation system carrying capacities by leaning over banks and 
growing into the water, thereby, trapping sediment. During canal 
drawdown, marginal weeds spread throughout the bottom making it 
essential to remove them prior to irrigation. The extensive root 
systems, stems, and leaves make these weeds difficult to control once 
they invade an area. Many of the species are so large that waterflow 
is restricted and tremendous quantities of water are wasted by 
transpiration. They also obstruct canal maintenance, thereby 
increasing costs to water users. 

Four common marginal plants found in the water systems of the 
western United States are explained in this section. For more 
information, consult the bibliography on page 89. 



Phalaris arudinacea L. 

Reed canarygrass is a slender, terrestrial plant which grows along 
sloughs, marshes, streambanks, and irrigation ditches. Although it is 
grown as a forage crop in some areas, it can be a nuisance in others. 
It grows in large clumps which lean out into irrigation ditches or 
actually grow into the water. This disrupts the waterflow and lowers 
the water carrying capacity of the irrigation ditches. 

Reed canarygrass can reach heights up to 1800 millimeters. The 
flowering head extends above the foliage, is pale gold when mature, 
and cylindrical in shape (insert 1) until the individual flowers spread 
out just prior to seeding. The grass forms dense mats of fibrous roots 
and yellowish-brown, creeping rootstocks (rhizomes). The flat, narrow 
leaves are soft, yellowish-green with prominent mid-veins on the 
underside, and come to a sharp point at the tips (insert 2). The leaves 
are hairless, and appear to be criss-crossed or hatched from a distance. 
Reproduction is by seed and by the extensive, creeping rootstocks 
which are difficult to control. 




Sorghum halepense L. Pers. 

Johnsongrass is a terrestrial plant which grows along the banks of 
irrigation ditches and on cultivated land. It is troublesome in fields, 
and can become so dense along ditchbanks that it will impede 
waterflow and lower the water carrying capacity of the irrigation 

This is a perennial grass which can reach heights of over 1800 
millimeters. The flat, narrow leaves have smooth margins, prominent, 
light-colored mid-veins, and can grow up to 500 millimeters in length. 
The loosely branched flower cluster is large, purplish in color and hairy 
(insert 2). Johnsongrass forms a fibrous root system, and stout, purplish 
rootstocks (rhizomes), which are usually scaly (insert 1). Reproduction 
is by the extensive, creeping rootstocks and prolific seed production, 
making this plant extremely difficult to control or eradicate. The 
rootstocks are able to withstand cold temperatures and the seed can 
lie dormant until more favorable growing conditions occur. 





Sorghum halepense 



Polygonum spp. 

Smartweed may be entirely aquatic, marginal, or amphibious; the 
same plant may even have portions under water with some branches 
erect on land. This extremely adaptable plant easily becomes a pest 
in irrigation systems and other bodies of water by displacing and 
transpiring large amounts of water. With approximately 320 species, 
smartweed grows under various ecological conditions around the world. 

The many species of smartweed share some common 
characteristics. The terrestrial forms are erect, or sometimes vine-like, 
but lack tendrils. The aquatic forms are emergent with floating leaves 
and stems. The stems of either forms can be simple or branched, but 
they usually have swollen joints and sheaths around the stem at each 
leaf base. The amount and type of plant hair varies tremendously 
among the species, however the aquatic forms are hairless. The simple, 
alternate leaves have smooth margins. Individual flowers are borne on 
short stalks which are clustered together along the main stem creating 
terminal spikelike floral structures (insert 1). The perfect flowers 
(having both male and female structures) have four to six petals and 
are pink, green, or white. The hard, dry, one-seeded fruits are either 
triangular or lens-shaped in cross section, and vary in color from 
light-tan through reddish-brown to black (insert 2). Roots can reach 
lengths of 9 to 15 meters, making control efforts very difficult. 

The seeds of smartweed are eaten by a variety of birds and small 
mammals. An aquatic area infested by smartweed is often a popular 
feeding area for waterfowl. 




Phragmites communis Trin. 

Common reed is abundant in marshes, along rivers, streams and 
canal banks. It is a terrestrial, perennial, and canelike grass with 
spreading pennant-like leaves. The reed often grows in dense stands 
in water or along the water's edge where it aids in stabilizing the bank, 
but becomes a nuisance by growing down into the water and impeding 
flow, and by absorbing and transpiring copious amounts of water. 

The reed has a thick stalk which reaches heights of 900 millimeters. 
The long, flat leaves spread out widely from the stem (insert 1), are 
relatively broad, but gradually narrow to a fine tip. The terminal 
plumelike flower cluster (insert 2) consists of numerous perfect flowers 
(having both male and female structures). Flowers are purple at first, 
but by maturity long, white silky hairs surround them, thus creating 
the large white feathery flower cluster visible throughout winter. 
Common reed also forms thick, creeping rhizomes (rootstocks) which 
forms the dense stands in and around bodies of water (insert 3). They 
are hardy structures which are primarily responsible for the difficulty 
in keeping common reeds under control. 



ai^p .,;„ 


# i 





■" 1 H 


r. [^^ 

Wi 1 j 


jS^l ^wH ' 

HI ^ i,^ 

-s. ■ ' i 

H ' ^^T 


f 1 

V fl *^^ 


f r7 

\ A'{' ; 

1 ■ 

, ( -; 






Invasion of woody plants on wet areas of irrigation systems is 
limited to a few species that tolerate wet or saturated soil areas, at least 
periodically. Most of these plants are referred to as phreatophytes, 
which is a term descriptive of plants that obtain their water supply 
from the soil saturation zone either directly or through the capillary 

Some of the woody weed species that fall in this category are 
saltcedar, cottonwood, willows, and wildrose. Although this grouping 
of weed plants deviates somewhat from the scope of true aquatic pests, 
they are included to emphasize their importance to the irrigator. 
Saltcedar is the one species that should be correctly identified in case 
of its invasion of a new area, because of its aggressiveness and apparent 
increasing range of adaption in the United States. 



Tamarix pentandra Pall. 

Saltcedar is a deciduous shrub or small tree that was apparently 
introduced into the United States as an ornamental shrub in the early 
1800's. A few species are still widely used as ornamental shrubs. The 
desert tamarisk or saltcedar, Tamarix pentandra , has become an 
aggressive invader and now occupies extensive areas on streams and 
flood plains of the Southwest. This species has created many pressing 
problems because of its rapid spread, producing dense growths that 
wastefully consume water in arid regions. Invasion of saltcedar has also 
produced serious problems by clogging floodway channels and 
increasing deposition of sediments. Saltcedar is considered to be a 

Tamarisk produces small, alternately arranged scalelike leaves 
(insert 1) that often become encrusted with salt secretions. The 
bushlike stems of younger plants are flexible and become 
brownish-purple as they age. The flowers range from pink to white and 
are clustered on branched flower stalks or panicles. The fruit is a 
capsule which may contain a varying number of seeds. The seeds have 
a tuft of hairs at the apex (insert 2), which aids in their wide 
dissemination. Saltcedar seedlings develop rather slowly, although the 
seeds germinate rapidly when deposited on moist soil. Both the 
seedling plant and older specimens will survive submergence periods 
of a few weeks. 

Taxonomy of species in this family has been subject to confusion 
in the past and is still in a stage of research. In general, T. pentandra 
is differentiated from similar species by the number of plant flower 
parts, particularly by stamens and petals, which are produced in fives 
(insert 3). This species is sometimes referred to as five-stamen 
tamarisk, from which the specific name pentandra is derived. 




S3I1X spp., PopuJus spp., Elaeagnus augustifolia h. 

Willow, Cottonwood, and russian olives will grow prolifically near 
most any body of freshwater and can particularly become pests along 
irrigation or drainage ditches. These woody plants consume large 
quantities of water, can degrade the canal lining, disrupt the water 
flow, trap sediment, and can become obstacles in the regular 
maintenance of irrigation systems. 

There are numerous species of willows ( Sali}^, all of which can be 
troublesome. Generally, the simple, alternate leaves are long and fairly 
narrow, widening slightly at the middle (insert 3). Most species have 
finely serrated leaf margins and some hair. The flowers are in catkins, 
but these can vary greatly according to the species. The willows 
produce numerous, small seeds each with a tuft of hair at their base. 

Cottonwoods {Populu^ are fast-growing deciduous trees which 
include a number of different species. Commonly they all have 
furrowed bark, stout branches, drooping catkins appearing before the 
leaves, numerous small seeds with tufts of hair, and simple leaves which 
grow alternately along the stems. The leaves vary from spear-shaped 
to egg- or triangular shaped (insert 2), but generally, the lower surfaces 
are paler in color than the upper. Cottonwood leaf margins are smooth 
to serrated, but somewhat serrated in most species. 

Russian-olive ( Elaeagnus augustifolid) is a deciduous shrub or small 
tree which is usually cultivated but sometimes escapes and becomes 
a pest. The leaves are roughly spear-shaped, approximately 35 to 75 
millimeters long, and olive-green in color (insert 1). Branches are 
reddish-brown when young and often have thorns, but as the older 
stems mature they become dark brown and very rough. The 
silvery-yellow fruits resemble small commercial olives, but are covered 
by tiny, silvery scales. These scales also cover the flowers, and 
undersides of the leaves and branches. 




In addition to various types of aquatic plant life found in irrigation 
systems, many small aquatic animals also present problems to water 
distribution. These animal pests, being of a relatively low order in the 
animal kingdom and therefore lacking an internal bone structure, are 
referred to as invertebrate animals. The aquatic animals of this type 
that create problems for the irrigation operator are submersed during 
some portion of their life cycle, usually attaching to submerged water 
structures or burrowing in the bottom mud of canals. Some of these 
more commonly observed animals are: Bryozoans or pipe moss, 
freshwater sponge, larvae of certain aquatic insects, and freshwater 

The problems that Bryozoa, sponge, and insect larvae create on 
irrigation structures are similar in scope to those produced by attached 
algae. These animals attach themselves to canal linings and other 
submerged water structures, creating considerable obstruction to 
waterflow. Also, the Bryozoa and sponge are often found growing 
inside of pipes and enclosed water conduits. The freshwater clam, 
while it does not attach to submerged water structures, does under 
certain conditions grow and develop so prolifically as to reduce the 
carrying capacity of a canal. Clams reduce the cross-sectional area of 
a canal by aiding in the rapid development of silt bars on the canal 

General descriptions of some of the typical invertebrate aquatic 
animals found in irrigation systems are given in the following pages 
to familiarize the reader with types that may be encountered. 



There is a single family of freshwater sponges, the Spongillidae. 
These are simple animals with bodies made up of unspecialized tissue 
without specific organs, consisting of a maze of interconnected 
channels, chambers, and orifices. The support or skeleton of the animal 
is mainly made up of random groups of needlelike siliceous bodies 
called spicules (insert 1) surrounded by gelatinous masses and 
sometimes a horny fiber called spongin. Spongin is the material that 
makes up the body of the commercial marine sponge. The spicule is 
useful in identifying this animal. 

The freshwater sponge is usually brown or yellowish in color; 
occasionally the animal has a greenish cast. This green coloration is 
produced by the unicellular algae that exist in the many chambers and 
channels of the sponge body and provide a food source for the animal. 
Water containing food materials is circulated through the many pores 
of the sponge by movement of threadlike projections or flagella. 

The size of the freshwater sponge is variable, depending on location 
and species. The sponge may be merely a slimelike or delicate mat 
becoming encrusted with the numerous outgrowths and branches; or, 
when new animals grow from year to year over the old, dead skeletons, 
the encrustation may attain considerable size. 

The animal is able to regenerate with a few cells, often 
overwintering in a perennial habit. The freshwater sponge produces 
a highly resistant resting body, or "gemmule" (insert 2), that is quite 
similar to the "statoblast" of Bryozoa. 

These animals are often found growing in clear, still water, and are 
being reported with increasing frequency as attached (sessile) growths 
in lined irrigation canals. 

Sponges in irrigation systems can cause considerable hydraulic 
problems when growing in association with other aquatic animals and 
plants. This undesirable effect is compounded by the favorable 
substrate they create for invasion of a wide variety of other aquatic 
pest organisms. 





The freshwater Bryozoa, or "pipe moss," are a group of 
invertebrate aquatic animals that are often mistaken for a mat of dead 
moss. Colonies of these animals are plantlike in appearance except for 
their coloration, which is brownish-white. Bryozoa attach to logs, 
rocks, and other submerged objects, usually where the light is relatively 
dim. They have been found on a number of irrigation systems growing 
in profusion on concrete canal linings, submerged inlet screens, 
louvers, trashracks, and on the inside of pipes (insert 1). The individual 
animal is microscopic, more or less cylindrical with a thin body wall. 
These animals secrete a thin protective layer about the body wall. 
Many of the individual animals grow in close association with one 
another to produce a connected, highly branched, antler-like colony 
(insert 2). The protective coatings of these colonies of animals are the 
most conspicuous feature, being massive and tough, or delicate and 
gelatinous, depending on the species. Oftentimes, young colonies 
continue to grow on the remaining protective layers of the dead 
animals, thus producing a thick mat on a solid substrate. 

The individual animals feed on various microscopic plants and 
animals that are swept into the animal's digestive system by a crown 
of tentacles. Tlie tentacles when extended have the appearance of tiny 
delicate flowers (insert 3A). A slight disturbance in the proximity of 
the animal will cause it to retract the tentacles in a flash. Most 
bryozoan colonies are stationary, but a few species are capable of 
sluggish movements. The colony can grow asexually where a portion 
of the body wall grows outward to produce a new animal. 

A unique feature of the Bryozoa is their ability to produce a highly 
resistant body called a statoblast or sessoblast (insert 3B). This seedlike 
body develops from asexual budding. This structure provides for the 
species to be carried over during unfavorable environmental conditions 
and for geographical disseminations. 

Bryozoa growing on submerged water structures and in conduits 
have been known to create serious hydraulic problems for water 
distribution structures. Two bryozoan species known to infest Water 
and Power Resources Service irrigation systems sufficiently to become 
problems are Plumatella repensL. and Fredericella sultana 
Blumenback. The latter species is illustrated. 




Corbicula fluminea , Muller 

The freshwater clam, or mussel, is quite extensive throughout 
inland waters of the United States. Species range from a few 
millimeters to over 100 millimeters in length. Many species have some 
commercial value, while others are troublesome pests. 

The Asiatic clam, Corbicula fluminea, is a species that has caused 
problems in irrigation systems in the Western United States by fouling 
pumps and inlet screens, plugging tubes of heat exchange devices, and 
reducing the carrying capacity of canals and conduits. These organisms 
have been reported in numerous areas of California, Arizona, and the 
Pacific Northwest; and some species of this genera are rapidly 
spreading into freshwaters of the Eastern United States. 

Members of the Corbicula genus are easily recognized by the 
distinctive concentric sculpture of the outer shell; but they are often 
overlooked until the population becomes dense, because of their habit 
of burying in the bottom mud. Some shells are thin and easily crushed 
while others are very thick. The shells of these animals are divided in 
halves or valves that are securely attached to each other by an elastic 
hinge. Under natural conditions, the valves open slightly to allow 
protrusions of the muscular foot at the lower margins of the shell. This 
foot provides for sluggish locomotion of the animal. 

The animal feeds on microorganisms which are drawn into the 
body cavity by an incurrent siphon. Wastes are excreted through a 
similar or excurrent siphon. These siphons can be seen barely 
protruding above the mud surface when the animal is feeding. During 
periods of disturbances or unfavorable environmental conditions, the 
animal will tightly close its shell halves and often bury itself deep into 
the soil. 

The species is reproduced by development and hatch of fertilized 
eggs within the adult clam. Individual clams may release thousands 
of microscopic larvae, which soon take up residence on the bottom 
strata. Little is known of the exact duration of the spawning season, 
which occurs chiefly in the summer months with a number of 
generations being produced in one season. 

A typical silt bar heavily infested with clams and remanent shells, 
as might be seen in a canal, is illustrated. The shells of Asiatic clams 
range from 35 to 50 millimeters in diameter when mature and vary 
in shape from somewhat triangular to oval. 




Siwulium spp. 

These insects belong to the family, Simuliidae, a small family which 
is classified in the fly order Diptera. The importance of this insect 
to the hydraulic factors of irrigation systems involves the pupal 
encasements, or cocoons, that are laid down on submerged canal and 
flume linings. These slipper-shaped encasements create extensive areas 
of roughened surfaces that increase resistance to waterflow in a canal. 

The adult fly is a small gnatlike insect that is seldom more than 
5 millimeters long, varying in color from gray-brown to black (insert 1). 
These insects are completely aquatic in all stages of their life cycle, 
except the free-flying adult which may be present in some areas in such 
great numbers as to be almost unbearable to a visitor. The "black fly," 
"buffalo gnat," or "no-see-ums" is well known for the persistent 
manner in which the female pursues and bites warm-blooded animals. 

In its life history, the adult fly deposits eggs on vegetation or other 
solid substrate just under the surface of swift water, especially where 
the current is broken. Overwintering sometimes occurs in the egg 
state. The eggs hatch below the water surface to produce larvae which 
attach themselves to a solid submerged substrate. The larval stage may 
last from 2 to 6 weeks. During the last stage of development, the larvae 
construct silken cocoons in which the insects develop into pupae, a 
growth stage preceding development and emergence of the adult. The 
cocoons are firmly cemented to the substrate and may be in the shape 
of a pocket, slipper, or vase (insert 2). Hiis is the growth stage that 
creates roughened surfaces on a canal lining. The pupae (insert 3A) 
are oval and enlarged at the upper end, and are yellow to red-brown 
in color. They have small abdominal hooks by which they remain 
attached to the cocoon (insert 3B). At the head end are two groups 
of long branched filaments extending out of the cocoons that perform 
as respiratory organs. The pupal stage usually last from 2 to 8 days prior 
to emergence of the flying adult. The pupal cases generally are quite 
persistent following emergence of the adult insects, and often require 
mechanical removal from canal linings. 

Identification of the genera and species of these insects is 
somewhat difficult, usually requiring detailed study of various portions 
of the insect body. These insects are widespread, but have been 
reported most commonly on irrigation structures in the Northwestern 
and the Rocky Mountain States. 




Aiken, S. G, P. R. Newroth, and I. Wile, "The Biology of Canadian 

Weeds, 34, Myriophyllum spicatum L." Canadian Journal of Plant 

Sciences, vol. 59, No. 1, Agricultural Insistitute of Canada, 

Ottawa, Ontario, pages 201-215, 1979. 
Correll, D. S. and H. B. Correll, "Aquatic and Wetland Plants of 

Southwestern United States," vol. 1 and 2, Stanford University 

Press, Stanford, Calif., pages 1-1777, 1975. 
Fassett, N. C, "A Manual of Aquatic Plants," The University of 

Wisconsin Press, Madison, page 346, 1960. 
Fernald, M. L., "The Linear Leaved North American Species of 

Potamogeton ,'' Memoirs of the American Academy of Arts and 

Sciences, Boston, Mass., vol. 17, part 1, page 1356, 1950. 
Fernald, M. L., "Gray's Manual of Botany," eighth edition, American 

Book Co., New York, N.Y., 1632 pages, 1950. 
Graves, A. H., "Ilustrated Guide to Trees and Shrubs," Harper and 

Row, New York, NY.; Evanston, 111.; and London, England, page 

186, 1956. 
Harrington, H. D., "Manual of the Plants of Colorado," Colorado 

State Board of Agriculture, The Swallow Press, Chicago, 111., pages 

22, 62, 195, 199, 387, 1954. 
Heikes, P. Eugene, "Colorado Weed Control Handbook," 

Cooperative Extension Service, Colorado State University, Fort 

Collins, Colo., 1962. 
Ingram, W. M. and A. F. Bartsch, "Animals Associated with Potable 

Water Supplies," Operators Identification Guide; AWWA 

Manual M7, American Water Works Association, New York, 

N.Y., page31, 1960. 
Mason, H. L. "A Flora of the Marshes of California," University of 

California Press, Berkeley and Los Angeles, page 878, 1957. 
Matsumura, Y. and H. D. Harrington, "The True Aquatic Vascular 

Plants of Colorado," Technical Bulletin 57, Colorado State 

University, Fort Collins, page 129, 1955. 
Muenscher, W. C, "Aquatic Plants of the United States," Comstock 

Publishing Association, Ithaca, N.Y., page 374, 1944. 
Nichols, S. A., "Identification and Management of Eurasian 

Watermilfoil in Wisconsin," Wisconsin Academy of Sciences, Arts 

and Letters, Madison, page 122, 1975. 
Oliver, Floyd, "Identification of Reed Canary Grass and Other 

Grasses Which May Be Mistaken for It," Bureau of Reclamation, 




Pennak, R. W., "Fresh-Water Invertebrates of the United States," 

The Ronald Press Company, New York, NY., page 769, 1953. 
Phillips Petroleum Company, "Introduced Crasses and Legumes," 

Section 5, Pasture and Range Plants, Phillips Petroleum Company, 

Bartlesville, Okla., page 24, 1958. 
Phillips Petroleum Company, "Introduced Grasses and Legumes," 

Section 6, Pasture and Range Plants, Phillips Petroleum Company, 

Bartlesville, Okla., page 14, 1960. 
Prescott, G. W., "Algae of the Western Great Lakes Area," Bulletin 

No. 31, Cranbrook Institute of Science, Bloomfield Hills, Mich., 

page 946, 1951. 
Prescott, G. W., "How to Know the Aquatic Plants," William C. 

Brown and Company, Dubuque, Iowa, pages 25, 76, 115, 117, 

Rotar, P. P., "Grasses of Hawaii," University of Hawaii Press, 

Honolulu, pages 119, 120, 216, 218, 219, 1968. 
Sinclair, R. M., "Clam Pests in Tennessee Water Supplies," AWWA 

Journal, vol. 56, No. 5, American Water Works Association, New 

York, N.Y., pages 592-599, 1964. 
Smith, G. M., "The Fresh-Water Algae of the United States," second 

edition, McGraw-Hill, New York, NY., page 719, 1950. 
Tennessee Valley Authority, "Hydrilla-A Waterweed Menace," 

Division of Environmental Planning, Water Quality, and Ecology 

Branch, Tennessee Valley Authority, Knoxville (pamphlet), 1977. 
United States Army Corps of Engineers, "Wetland Plants of the New 

Orleans District,", U.S. Army Corps of Engineers, New Orleans, 

Louisiana, pages 21, 22, 38, 1977. 
University of Illinois, "Weeds of the North Central States," revised 

edition. North Central Regional Publication No. 36, Circular 718, 

Agricultural Experiment Station, University of Illinois, Urbana, 

page 30, 1960. 
Whipple, G. C., "Microscopy of Drinking Water," revised by G. M. 

Fair and M. C. Whipple, fourth edition, John Wiley and Sons, 

New York, N.Y.; Chapman and Hall, Ltd., London, England, page 

585, 1954.